i) Field of the Invention
The present invention relates to a piezoelectric actuator, and an information storage apparatus in which the piezoelectric actuator is used.
ii) Description of Related Art
As an information storage apparatus built in or connected to electronic apparatuses such as a personal computer and a word processor, a hard disk drive has been heretofore known. The hard disk drive is generally provided with a disk as an information storage medium, and a head for reading/writing a recording bit with respect to the disk, and is also provided with an arm for holding the head in the vicinity of the disk, and an electromagnetic actuator for driving the arm to move the head along the disk.
A recording density of the hard disk drive has increased with development of the personal computer or the like, and particularly in recent years, has rapidly increased with an increasing demand for handling of image or music with the personal computer or the like. Moreover, with enhancement of the recording density of the hard disk drive, recording bit on the disk has been finely divided, disk rotation speed has increased, and high precision and high rate in positioning the head have been requested. Furthermore, miniaturization, lightening and power saving of the hard disk drive have also been promoted.
Therefore, in order to position the head at high precision and high rate, a hard disk drive has been proposed in which a piezoelectric actuator independent of the conventional electromagnetic actuator is disposed midway on the arm.
However, the heretofore proposed piezoelectric actuator and hard disk drive have problems that sufficient displacement cannot be obtained, drive voltage is high, dimension and weight are large, inertia moment during head driving is large, and manufacture cost is high.
These problems are not generated only in the hard disk drive, and are generally generated with respect to the information storage apparatus in which the head is held and moved by the arm.
The present invention has been developed in consideration of the aforementioned situations, and an object thereof is to provide a piezoelectric actuator in which large displacement is obtained at low voltage, which is small-sized and lightweight, and whose manufacture cost is low, and an information storage apparatus in which the piezoelectric actuator is incorporated, whose inertia moment during head driving is small, and which is high in recording density, small-sized and lightweight.
In order to achieve the aforementioned object, according to the present invention, there is provided a first piezoelectric actuator comprising:
a piezoelectric layer which is formed of a piezoelectric material of a two-dimensional shape provided with a central portion, and a group of arm portions extended to the outside from the central portion in rotation symmetry and nonlinear symmetry, and which is compressed/extended in an in-layer direction; and
a plurality of electrode layers for holding the piezoelectric layer.
Here, the piezoelectric layer may be a flat layer having the two-dimensional shape, or a layer curved in the two-dimensional shape.
When a voltage is applied to the piezoelectric layer, the piezoelectric layer is contracted in the in-layer direction. In this case, if tip ends of respective arm portions constituting the arm portion group are fixed to a common rigid body, because of the two-dimensional shape, the central portion largely rotates at a low voltage. Moreover, since the structure of the first piezoelectric actuator of the present invention is easily manufactured, the first piezoelectric actuator can inexpensively be manufactured as a small-sized lightweight actuator.
In the first piezoelectric actuator of the present invention, the arm portion constituting the arm portion group is preferably turned to a backside via the central portion with respect to a root by which the arm portion is connected to the central portion.
Moreover, the first piezoelectric actuator of the present invention is preferably provided with a plurality of the piezoelectric layers.
For the piezoelectric actuator including the arm portion turned to the backside of the central portion, rotation amount of the central portion is large for contraction amount of the arm portion. For the piezoelectric actuator provided with a plurality of piezoelectric layers, the contraction amount of the piezoelectric layer is large for the voltage applied between the electrode layers. Therefore, by these piezoelectric actuators, larger displacement can be obtained at a lower voltage.
When the first piezoelectric actuator of the present invention is provided with a plurality of piezoelectric layers, the plurality of the electrode layers of the same potential are preferably connected to one another by a via hole.
The piezoelectric actuator employing the via hole as means for connecting the electrode layers to one another is easy in manufacture and low in manufacture cost.
Moreover, in the first piezoelectric actuator of the present invention, the piezoelectric layer is formed preferably of lead zirconate titanate (PZT) based piezoelectric ceramic, more preferably of PNN-PT-PZ based piezoelectric ceramic.
As the piezoelectric material for forming the piezoelectric layer, PZT, PT, barium titanate, layered perovskite and other piezoelectric materials can be utilized, but PZT based piezoelectric ceramic is inexpensive, large in piezoelectric constant, and suitable as the piezoelectric material for forming the piezoelectric layer. Particularly, a PNN-PT-PZ based piezoelectric material indicates a particularly high piezoelectric constant among the PZT based piezoelectric materials, is superior in sinterability and is therefore particularly preferable as the piezoelectric material to form the piezoelectric layer.
To achieve the aforementioned object, according to the present invention, there is provided a second piezoelectric actuator comprising:
a driving portion provided with a lamination structure including at least one piezoelectric layer of a piezoelectric material and a plurality of electrode layers for holding the piezoelectric layer, and compressed/extended in a lamination direction of the lamination structure; and
a holding portion for holding a plurality of the driving portions in an arrangement of rotation symmetry and nonlinear symmetry including the lamination direction in a predetermined common plane.
For the second piezoelectric actuator of the present invention, when the plurality of driving portions held by the holding portion are all compressed/extended, the aforementioned arrangement causes large rotation displacement at a low voltage. Moreover, since the structure of the second piezoelectric actuator of the present invention is easily manufactured, the second piezoelectric actuator can inexpensively be manufactured as the small-sized lightweight actuator.
The second piezoelectric actuator of the present invention is typically provided with two driving portions, and the typical second piezoelectric actuator is provided with an immobile portion adjacent to the driving portion in a direction intersecting the direction in which the driving portion is compressed/extended,
Wherein the holding portion holds two pairs of the driving portion and the immobile portion opposite to each other in such a manner that the driving portion of one pair turns the compressed/extended direction of the driving portion to the immobile portion of the other pair.
Moreover, for the typical second piezoelectric actuator of the present invention, the holding portion preferably holds two pairs of the driving portion and the immobile portion in such a manner that the driving portion is disposed opposite to the immobile portion via a slit.
According to the piezoelectric actuator in which the driving portion is disposed opposite to the immobile portion via the slit in this manner, the driving portion is easily compressed/extended, and larger displacement can be obtained at a lower voltage.
To achieve the aforementioned object, according to the present invention, there is provided a first information storage apparatus comprising:
a head portion on which a head for performing at least one of information recording and information reproduction with respect to a predetermined information storage medium is mounted;
an arm portion for holding the head portion in such a manner that the head mounted on the head portion is disposed in the vicinity of or in contact with the information storage medium;
an arm portion actuator for driving the arm portion to move the head mounted on the head portion held by the arm portion along the information storage medium; and
a head portion actuator for rotating the head portion with respect to the arm portion and centering on a gravity center of the head portion,
Wherein the head portion actuator comprises:
a piezoelectric layer which is formed of a piezoelectric material of a two-dimensional shape provided with a central portion, and a group of arm portions extended to the outside from the central portion in rotation symmetry and nonlinear symmetry, and which is compressed/extended in an in-layer direction; and
a plurality of electrode layers for holding the piezoelectric layer.
Here, the head may be a magnetic head or an optical head.
For the first information storage apparatus of the present invention, the head portion includes the head, and a slider, with the head mounted thereon, for sliding on the information storage medium, the arm portion includes the arm driven by the arm portion actuator and a suspension connected to the arm, and the head portion actuator may be disposed between the suspension and the slider.
Alternatively, for the first information storage apparatus of the present invention, the head portion includes the head, the slider, with the head mounted thereon, for sliding on the information storage medium, and a suspension for holding the slider, and the head portion actuator may be disposed between the suspension and the arm portion.
According to the first information storage apparatus of the present invention, since the head portion is rotated centering on the gravity center by the head portion actuator, the inertia moment during head driving is small, and head position can highly precisely be controlled. Moreover, the head portion actuator is a small-sized lightweight actuator similar to the first piezoelectric actuator. Therefore, the first information storage apparatus of the present invention is realized as a small-sized lightweight apparatus with a high recording density.
Moreover, for the first information storage apparatus of the present invention, the head portion actuator is preferably joined to the arm portion by a portion corresponding to the tip end, of the arm portion constituting the arm portion group, extending from the central portion, and joined to the head portion by a portion corresponding to the central portion. Furthermore, in the preferably constituted information storage apparatus, the electrode layer is preferable in that voltage is applied to the head portion actuator in its portion connected to the arm portion. The preferably constituted information storage apparatus is easily manufactured.
To achieve the aforementioned object, according to the present invention, there is provided a second information storage apparatus comprising:
a head portion on which a head for performing at least one of information recording and information reproduction with respect to a predetermined information storage medium is mounted;
an arm portion for holding the head portion in such a manner that the head mounted on the head portion is disposed in the vicinity of or in contact with the information storage medium;
an arm portion actuator for driving the arm portion to move the head mounted on the head portion held by the arm portion along the information storage medium; and
a head portion actuator for rotating the head portion with respect to the arm portion and centering on a gravity center of the head portion,
Wherein the head portion actuator comprises:
a driving portion provided with a lamination structure including at least one piezoelectric layer of a piezoelectric material and a plurality of electrode layers for holding the piezoelectric layer, and compressed/extended in a lamination direction of the lamination structure; and
a holding portion for holding a plurality of the driving portions in an arrangement of rotation symmetry and nonlinear symmetry including the lamination direction in a predetermined common plane.
Additionally, for the head portion actuator referred to in the information storage apparatus of the present invention, only a basic mode is described herein, but this simply avoids redundancy, and the head portion actuator referred to in the information storage apparatus of the present invention includes not only the basic mode of the head portion actuator but also various modes of head portion actuators applied to the aforementioned respective modes of the piezoelectric actuator.
Moreover, also for the second information storage apparatus of the present invention, to avoid redundant description, only the basic mode is described, but the second information storage apparatus of the present invention includes various modes of the second information storage apparatus applied to the respective modes of the first information storage apparatus.